The acicular strontium carbonate particles can be incorporated into polymer resin to cancel birefringence of the polymer resin or to give birefringence to the polymer resin. The polymer resin composition of which birefringence is cancelled can be employed for the use as non-birefringent optical resin material or transparent plate. The polymer resin composition which is given birefringence can be employed as retardation plate.
D1(JP 2004-35347 A) describes that a non-birefringent optical resin material can be manufactured by dispersing in polymer material acicular strontium carbonate particles having a length of 500 nm or less under such condition that the length of the acicular strontium carbonate particles are aligned in parallel or perpendicular to the extended bonding chain of the polymer resin so as to cancel the birefringence brought about by the extension of the bonding chain. D1 further describes that the above-mentioned acicular strontium carbonate particles can be manufactured by chilling a mixture of an aqueous strontium salt solution and urea below the freezing point to hydrolyze the urea in the aqueous solution or by the steps of chilling an aqueous strontium hydroxide suspension below the freezing point and introducing gaseous carbon dioxide into the aqueous suspension. D1 discloses in Example 3 that acicular strontium carbonate particles having a mean length of 200 nm or less were manufactured by the above-mentioned procedures.
D2(JP 2008-247692 A) describes fine acicular strontium carbonate particles are manufactured by the steps of placing an aqueous solution containing a carbonate source in an alcohol containing a strontium ion source and then reacting strontium with the carbonate source in the presence of an alkaline agent. D2 contains a working example describing that acicular strontium carbonate particles having a mean length of 200 nm or less were manufactured by the above-mentioned procedures.
D3(JP 2010-254533 A) describes stick-like fine strontium carbonate particles are manufactured by the steps of reacting strontium hydroxide with a carbonate source such as carbon dioxide or a water-soluble carbonate in an aqueous medium in the presence of a particle growth-controlling agent selected from the group consisting of polyhydric alcohols, pyrophosphoric acid, ascorbic acid, carboxylic acids, carboxylates, polycarboxylic acids, and polycarboxylates, whereby producing acicular strontium carbonate particles, and heating the resulting acicular strontium carbonate particles in water to a temperature of 50° C. or higher. An example of the polycarboxylic acid is polyacrylic acid. D3 contains a working example in which stick-like strontium carbonate particles having a mean length of 200 nm or less were manufactured by the above-mentioned procedures. D3 has such description that the stick-like strontium carbonate particles manufactured by the disclosed procedure have a weak contracted portion and, owing to the presence of the weak portion, spherical particles can be easily obtained from the stick-like particles by pulverization procedures such as an airflow-type pulverizer.